As an antivibration device for supporting and fixing a vibration generator such as an automotive engine or transmission so as not to transmit its vibration to a vehicle body frame, a hydraulic style antivibration device is well known.
This hydraulic antivibration device is, in general, made up of a first attachment fitting designed to be attached to an engine side and a second attachment fitting to be attached to a vehicle body frame side, wherein both attachment fittings are interconnected by a vibration-isolating base composed of a rubber-like elastomer. At the second attachment fitting a diaphragm is attached, whereby between the diaphragm and the vibration-isolating base there is formed a liquid-filled chamber.
The liquid-filled chamber is divided by a partitioning means into a first liquid chamber and a second liquid chamber, both of which are put into communication with each other through an orifice. According to this hydraulic antivibration device, a fluidization effect of a fluid between the first liquid chamber and the second liquid chamber and a vibration deadening effect of the vibration-isolating base perform a vibration damping function and a vibration insulating function.
There exists another hydraulic antivibration device, such that the partitioning means is constructed of an elastic partition membrane and a pair of displacement-regulating members regulating the displacement amount of the elastic partition membrane from its both sides.
According to the hydraulic antivibration device of this style, when a relatively small amplitude vibration is input, the elastic partition membrane reciprocates to be displaced, thereby absorbing the hydraulic pressure fluctuations between both liquid chambers, whereby a low dynamic spring characteristic is obtainable. On the other hand, when a relatively large amplitude vibration is input, for example, owing to irregular road surfaces upon travelling, the displacement-regulating members serve to regulate the displacement amount of the elastic partition membrane from both sides to raise the stiffness of the membrane thereby to facilitate fluidization of fluid between both liquid chambers through the orifice, so that a high damping characteristic can be obtained.
However, a problem with this style of hydraulic antivibration device was that because of the construction that the elastic partition membrane is struck (made into abutment) on the displacement-regulating members, the displacement-regulating members oscillate at the time of striking, which oscillation is transmitted to the vehicle body frame and results in generation of strange sounds.
To address this problem, for example, the thickness of the membrane is made larger or the hardness of the rubber is made higher, thereby heightening the membrane stiffness of the elastic partition membrane to make it difficult for the elastic partition membrane to do reciprocating displacement, whereby the striking of the membrane on the displacement-regulating members can be precluded to suppress the generation of strange sounds. In this case, however, the elastic partition membrane is difficult to deform, complying with the hydraulic pressure fluctuations between both liquid chambers, so that it becomes difficult to absorb the hydraulic pressure fluctuations and it is unable to obtain a low dynamic spring characteristic.
In the circumstances, heretofore, the contact area of the elastic partition membrane with the displacement-regulating members has been made small by providing the displacement-regulating members with radial ribs, whereby the generation of strange sounds has been suppressed, as disclosed, for example, in JP Patent Publication 6-221368A (Patent Reference 1).                [Patent Reference 1] JP Patent Application Publication 6-221368A (FIG. 4, etc.)        